Processes for the production of composite plastic parts, e.g., with a cellular core and a solid surface layer, are already known.
A process described in German Auslegeschrift No. 2,127,582 is said to result in composite parts with cellular cores and flawless non-cellular surfaces, by the successive introduction of several substances into a closed mold having a rigid cavity. In this process, at least one foamable plastic charge and a second plastic charge which may be either foamable or unfoamable are used, with the second charge forming the part's surface after compression of the first charge. The time sequence is chosen such that the second charge will not permeate the first charge but will compress the first charge according to its mass or volume, and form a good chemicophysical bond with the first filling, because the first charge is not yet fully reacted and has still a sufficient tackiness and is still compressable.
This process has made obsolete the practice of "wrapping" (enclosing) a poIymer which contains a blowing agent with a polymer which does not contain a blowing agent. It is also no longer necessary to expand the cavity of a mold, by enabling the mold to "breathe" (see German Auslegeschrift No. 2,442,227), in order to produce a composite plastic article.
In German Auslegeschrift No. 2,127,582, three examples describe combinations of polyurethane plastics of differing structure and hardness, as well as combinations of polyurethane plastics with polymerization and polycondensation plastics. These examples are limited to a description of the process of filling the cavity of the mold, in which the number and position of the mixing heads used may vary. Thus, composite parts produced from a first charge of a foamable polyurethane foam, which should have facilitated release from the mold due to its hardness, and a second charge of a foamable or elastomeric lightfast, colorfast, weather-resistant polyurethane plastic could not be removed from the mold cavity without damage to the composite part.
It is an object of the present invention to provide a process for the production of a lightfast, colorfast, weather-resistant composite part from cellular plastics containing urethane and/or isocyanurate groups, which releases from the mold without difficulties. This problem is solved by the present invention.